Solid propellant compositions containing iron catalyst



y 1, 1965 A. E. LEMKE 3,183,133

SOLID PROPELLANT COMPOSITIONS CONTAINING IRON CATALYST Filed 001. 21. 1960 ---=8.6% IRON lo ---coN"rRoL-No IRON 2 3 Q E- E i g I:

2 .7 z .6 z g .5

I5 20 3O 40 5060 80 I00 200 300 400 600 800 I000 CHAMBER PRESSURE-PSIA INVENTOR.

ALBERT E. LEMKE BY 0%.

ATTORNEY United States Patent 015cc Ohio Filed Oct. 21, 1960, Ser. No. 64,220 '10 Claims. (Cl. 149-40) This invention relates to solid propellants and has for its object to improve the burning rates and properties of such propellants. In particular, it relates to solid propellant compositions useful for underwater propulsion and ignition devices.

Propellant compositions heretofore employed for propelling underwater projectiles have been intimate mixtures of finely divided inorganic oxidizing salts such as the chlorate, perchlorate, chromate, or dichromate salts of a metal dispersed in a finely divided, readily oxidizable metal capable of liberating large quantities of heat during oxidation, such as beryllium, aluminum, or mag nesium. These propellant compositions are particularly adapted for underwater military use since they do not produce noncondensable gases upon combustion. Such gases create a highly undesirable visible wake. Due to their compactness and nongassing properties, such propellants also find valuable use in burning and cutting metal such as pipe in oil wells. Unfortunately, however, the combustion of such propellants becomes unstable at high pressures and this feature seriously limits the conditions under which these propellants may be used either for underwater propulsion or cutting purposes.

In underwater operation such propellants are burned in the presence of water and the driving thrust is created by means of evaporating the water to steam. The magnitude of the thrust is dependent upon the amount of heat available for generating steam during the time the projectile is in motion. The amount of available heat is in turn dependent upon the properties of the particular propellant being burned as well as the amount of the propellant consumed. In underwater projectiles the burning area of a propellant is confined to a given cross section due to space limitations inherent in the design of such projectiles. Thus, in order to increase the thrust created by burning such a propellant, it is necessary to increase the linear buming rate of the propellant.

I have now found that the pressure stability during combustion as well as the burning rate of such propellants is greatly increased and improved by incorporating finely divided iron into the propellant composition. Such finely divided iron in amounts as small as about 1 percent by weight of the propellant substantially increases its linear burning rate and greatly improves its pressure stability during combustion.

The iron additive is incorporated into the propellant merely by mechanically mixing it with the other ingredients, all being in finely divided form, until an intimate and uniform mixture is obtained. Optimum results are achieved when the iron is employed in amounts of from about 1 percent to about 30 percent by weight of the propellant and the readily oxidizable metal and inorganic oxidizing salts are in approximately stoichiometirc proportions.

The readily oxidizable metals commonly employed in the propellant composition release large quantities of heat during oxidation, have a high positive electrode potential, and are stable in the presence of air under ordinary conditions. Metals such as beryllium, aluminum, and magnesium which exhibit electrode potentials in excess of +1.6 volts at 25 C. and which liberate at least 2.4 kcaL/gram when reacted with perchlorates are preferred. The oxidizing salt usually employed is a chlo- Patented May 11, 1965 rate, perchlorate, chromate, or dichromate salt of a metal, or mixturesof such salts. For reasons of com venience and weight, the alkali and alkaline earth metal salts are preferred. The perchlorate salts are preferred due to their light weight, stability, and high oxygen content.

The basic solid propellants into which iron is incoraporated to effect an improvement according to this invention are prepared by mixing the finely divided metal and finely divided inorganic oxidizing salt until an intimate, uniform mixture is obtained. The mixture is then compressed under high pressure to obtain the solid grain. The preferred formulations of the propellant compositions which have been found to be particularly useful for underwater jet propulsion are shown in Table I.

Table 1 Propellant Constituents I By Weight Percent A Aluminum Potasiium perchloratc.- n

Beryllium Sodium perchlorate.

Magnesium Sodium perchlorate To illustrate the effect of the addition of iron to the basic propellants examplified by the Table I formulations, burning rate vs. chamber pressure data for a control propellant formulation and for one with the iron additive of this invention are presented in the form of burning rate curves in FIGURE 1. The control propellant formulation consisted of stoichiometric equivalents of finely divided aluminum and potassium perchlorate. The iron-containing formulation differed from the control only in that it contained finely divided iron, uniformly distributed throughout, in an amount equivalent to 8.6 percent of the total propellant weight.

It is evident from a comparison of the FIGURE 1 curves that throughout almost the entire range of pressures tested the burning rate of the iron-containing prw pellant of this invention was greater than that of the control and that at lower'pressures it was substantially greater. For example, at a chamber pressure of p.s.i.a. the burning rate of my novel propellant was almost four times greater than that of the control. Of perhaps equal importance, however, as those skilled in the art will appreciate, the FIGURE 1 curves indicate that the control propellant was unstable at chamber pressures greater than 100 p.s.i.a. whereas the iron-containing propellant was stable at all pressures under which it was tested. By stability, as the term is employed in the propellant art, is meant the ability of the propellant to burn without wide pressure fluctuations.

The FIGURE 1 curves represent plots of the empirical equation r=Cp for the propellant formulations tested. In the above equation, r is the burning rate, p is absolute pressure (p.s.i.a.), and C and n are constants. The burn- Table II Chamber Additive Pressure Stability Range Factor (n) (p.s.l.a.)

It will be readily apparent from the FIGURE 1 curves and the data of Table II that throughout the range of chamber pressures shown the iron-containing propellant of this invention exhibited excellent or acceptable (depending upon the chamber pressure value) stability whereas the control propellant was sutficiently stable only at pressures lower than 100 p.s.i.a.

The primary advantage to the use of iron as an additive in the propellants of this invention is the fact that such use results in substantially higher burning rates, which means that more fuel will burn in a given period of time with a resulting increase in thrust. In addition, the use of iron provides a substantial improvement in pressure stability permitting a broader range of operating conditions to be attained.

While the compositions of this invention have been referred to throughout this application as solid propellants, they have utility for many other purposes besides that of propelling underwater projectiles. For example, the novel compositions of this invention can be employed as a pyrotechnic charge for many applications such as, for example, as a charge for pyrotechnic flares. Furthermore, due to the large amount of energy generated by the combustion of the compositions of this invention, they find utility as ignitcr charges for use in the ignition systems of rocket motors. Since the material produces an extremely highflame temperature upon burning it liberates sufficient heat to vaporize all of the combustion product and deliver the required ignition pressures. For this reason, the compositions of this invention have particular utility as a charge for igniters of the type which do not require nozzle closure members such as that more fully described in assignees copending US. patent application Serial No. 306,- 030, filed August 23, 1952, now US. Patent No. 3,000,- 312, issued September 19, 1961. As those skilled in the art will readily appreciate, the relatively high burning rate and stability of my novel propellant compositions are of great advantage insofar as igniter utility is concerned- It is apparent from the above discussion that by incorporating finely divided iron into propellant compositions containing finely divided metals such as beryllium, magnesium, or aluminum and inorganic oxidizing salts, propellants which provide greater thrust when used for underwater propulsion are obtained. In addition, these propellants may be used under a wide range of pressures, thus greatly increasing their usefulness both for underwater propulsion and for burning and cutting operations in oil wells. The improved propellants of this invention are particularly suited for use in underwater propulsion plants of the type disclosed in assignees copending US. application Serial No. 428,698, filed May 10, 1954, now abandoned. It it within the scope of my invention to employ iron as an additive for propellants of the type disclosed herein in conjunction with other additives such as, for example, lead if desired. It is also within the scope of the invention to employ mixtures of suitable metals such as beryllium, aluminum, and magnesium as well as mixtures of oxidizing salts in my novel propellants or, as they are more properly called, pyrotechnic compositions.

I claim:

1. In a pyrotechnic composition consisting essentially of an intimate mixture of readily oxidizable metal selected from the group consisting of beryllium, aluminum, and magnesium and an inorganic oxidizing material selected from the group consisting of the alkali and alkaline earth metal chlorates, perchlorates, chromates, dichromates, and mixtures thereof; the improvement which comprises the intimate dispersion of finely divided iron therein as a burning rate acceleration additive, said finely divided iron being present in an amount of from about 1 percent to about 30 percent of the total pyrotechnic composition.

2. A pyrotechnic composition consisting essentially ot readily oxidizable metal selected from the group consisting of beryllium, aluminum, magnesium, and mixtures thereof in substantially stoichiometric proportion with an inorganic oxidizing material selected from the group consisting of the alkali and alkaline earth metal chlorates, perchlorates, chromates, dichromates, and mixtures thereof and, as a burning rate acceleration additive, finely divided iron in an amount of from about 1 percent to about 30 percent by weight of the total pyrotechnic composition.

3. A pyrotechnic composition consisting essentially of an intimate mixture of finely divided aluminum, an alkali metal perchlorate, and finely divided iron, the iron being present in an amount of from about 1 percent to about 30 percent by weight of the total pyrotechnic composition.

4. A pyrotechnic composition consisting essentially of an intimate mixture of a finely divided aluminum and an alkali metal perchlorate in substantially stoichiometric proportions and finely divided iron in an amount of from about 1 percent to about 30 percent of the total pyrotechnic composition.

5. A pyrotechnic composition consisting essentially of an intimate mixture of finely divided aluminum and potassium perchlorate in substantially stoichiometric proportions and finely divided iron in an amount from about 1 percent to about 30 percent by weight of the total pyrotechnic composition.

6. The pyrotechnic composition of claim 5 in which the finely divided iron is present in an amount equivalent to 8.6 percent by weight of the total pyrotechnic cornposition.

7. In a solid pyrotechnic composition consisting essentially of an intimate mixture of a metal having an electrode potential above +1.6 volts at 25 C. and which will liberate at least 2.4 kcal./gram when reacted with perchlorates, and an inorganic oxidizing material selected from the group consisting of the alkali and alkaline earth metal chlorates, perchlorates, chromates, dichromates, and mixtures thereof; the improvement which comprises incorporating therein as a burning rate acceleration additive, finely divided iron in an amount of from about 1 percent to about 30 percent by weight of the total pyrotechnic composition.

8. In a solid pyrotechnic composition consisting essentially of an intimate, uniform, highly compressed mixture of a metal having an electrode potential above +1.6 volts at 25 C. and which will liberate at least 2.4 kcal./ gram when reacted with perchlorates, and an inorganic oxidizing material selected from the group consisting of the alkali and alkaline earth metal chlorates, perchlorates, chromates, dichromates, and mixtures thereof; the improvement which comprises incorporating therein as a burning rate acceleration additive, finely divided iron in an amount of from about 1 percent to about 30 percent by weight of the total pyrotechnic composition.

9. A solid pyrotechnic composition consisting of an intimate mixture of a metal having an electrode potential above +1.6 volts at 25 C. and which will liberate at least 2.5 kcal./gram when reacted with perchlorates, and an inorganic oxidizing material selected from the group consisting of the alkali and alkaline earth metal chlorates, perchlorates, chromates, dichromates, and mixtures thereof, and as a burning rate acceleration additive, finely divided iron in an amount of from about 1 percent to about 30 percent by weight of the total pyrotechnic composition.

10. A solid pyrotechnic composition consisting of an intimate uniform highly compressed mixture of a metal having an electrode potential above +1.6 volts at 25 C. and which will liberate at least 2.5 kcaL/grarn when reacted with perchlorates, an inorganic oxidizing material selected from the group consisting of the alkali and alkaline earth metal chlorates, perchlorates, ohrcmates, dichromates, and mixtures thereof, and containing uniform- 1y dispersed throughout said composition as a burning rate acceleration additive, finely divided iron -in an amount of from about 1 percent to about 30 percent by weight of the total pyrotechnic composition.

References Cited by the Examiner UNITED STATES PATENTS FOREIGN PATENTS Great Britain. Great Britain.

15 REUBEN EPSTEIN, Primary Examiner.

CARL D. QUARFORTH, LEON D. ROSDOL,

Examiners. 

1. IN A PYROTECHNIC COMPOSITION CONSISTING ESSENTIALLY OF AN INTIMATE MIXTURE OF READILY OXIDIZABLE METAL SELECTED FROM THE GROUP CONSISTING OF BERYLLIUM, ALUMINUM, AND MAGNESIUM AND AN INORGANIC OXIDIZING MATERIAL SELECTED FROM THE GROUP CONSISTING OF THE ALKALI AND ALKALINE EARTH METAL CHLORATES, PERCHLORATES, CHROMATES, DICHROMATES, AND MIXTURES THEREOF; THE IMPROVEMENT WHICH COMPRISES THE INTIMATE DISPERSION OF FINELY DIVIDED IRON THEREIN AS A BURNING RATE ACCELERATION ADDITIVE, SAID FINELY DIVIDED 